Luteinizing hormone, oestrogen and progesterone levels in peripheral serum of anoestrous and cyclic ewes as determined by radioimmunoassay

Abstract

Jugular vein blood was collected daily from mature ewes throughout anestrus and the first estrous cycle of the breeding season until 4 days after the second estrus. The levels of estrogen, progesterone and (LH) were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anestrous period with a mean ± S.E. value of 2.3 ± 0.9 ng/ml. High LH values of 20.0, 41.2 and 137.5 ng/ml were observed in three ewes on day -24 of anestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0.11 ± 0.01 ng/ml) before day -25 of anestrus. A major rise occurred on day -12 of anestrus and this was followed by patterns similar to those that have been previously reported for the estrous cycle of the ewe. Random fluctuations of estrogens deviating from a mean level of 4.40 ± 0.1 pg/ml were observed during anestrus and the mean level during the period from the first to the second estrus was 5.2 ± 0.3 pg/ml. A well defined peak of 13.3 ± 0.7 pg/ml was seen in all ewes on the day of the second estrus. Results of the present study suggest that episodic releases of LH occur during anestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day -25 of anestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural estrus of the breeding season is supported.